This invention relates to uracyl spirooxetane nucleosides that are inhibitors of the hepatitis C virus (HCV).
HCV is a single stranded, positive-sense RNA virus belonging to the Flaviviridae family of viruses in the hepacivirus genus. The NS5B region of the RNA polygene encodes a RNA dependent RNA polymerase (RdRp), which is essential to viral replication. Following the initial acute infection, a majority of infected individuals develop chronic hepatitis because HCV replicates preferentially in hepatocytes but is not directly cytopathic. In particular, the lack of a vigorous T-lymphocyte response and the high propensity of the virus to mutate appear to promote a high rate of chronic infection. Chronic hepatitis can progress to liver fibrosis, leading to cirrhosis, end-stage liver disease, and HCC (hepatocellular carcinoma), making it the leading cause of liver transplantations. There are six major HCV genotypes and more than 50 subtypes, which are differently distributed geographically. HCV genotype 1 is the predominant genotype in Europe and in the US. The extensive genetic heterogeneity of HCV has important diagnostic and clinical implications, perhaps explaining difficulties in vaccine development and the lack of response to current therapy.
Transmission of HCV can occur through contact with contaminated blood or blood products, for example following blood transfusion or intravenous drug use. The introduction of diagnostic tests used in blood screening has led to a downward trend in post-transfusion HCV incidence. However, given the slow progression to the end-stage liver disease, the existing infections will continue to present a serious medical and economic burden for decades.
Current HCV therapy is based on (pegylated) interferon-alpha (IFN-α) in combination with ribavirin. This combination therapy yields a sustained virologic response in more than 40% of patients infected by genotype 1HCV and about 80% of those infected by genotypes 2 and 3. Beside the limited efficacy against HCV genotype 1, this combination therapy has significant side effects and is poorly tolerated in many patients. Major side effects include influenza-like symptoms, hematologic abnormalities, and neuropsychiatric symptoms. Hence there is a need for more effective, convenient and better-tolerated treatments.
Experience with HIV drugs, in particular with HIV protease inhibitors, has taught that sub-optimal pharmacokinetics and complex dosing regimes quickly result in inadvertent compliance failures. This in turn means that the 24 hour trough concentration (minimum plasma concentration) for the respective drugs in an HIV regime frequently falls below the IC90 or ED90 threshold for large parts of the day. It is considered that a 24 hour trough level of at least the IC50, and more realistically, the IC90 or ED90, is essential to slow down the development of drug escape mutants. Achieving the necessary pharmacokinetics and drug metabolism to allow such trough levels provides a stringent challenge to drug design.
The NS5B RdRp is essential for replication of the single-stranded, positive sense, HCV RNA genome. This enzyme has elicited significant interest among medicinal chemists. Both nucleoside and non-nucleoside inhibitors of NS5B are known. Nucleoside inhibitors can act as a chain terminator or as a competitive inhibitor, or as both. In order to be active, nucleoside inhibitors have to be taken up by the cell and converted in vivo to a triphosphate. This conversion to the triphosphate is commonly mediated by cellular kinases, which imparts additional structural requirements on a potential nucleoside polymerase inhibitor. In addition this limits the direct evaluation of nucleosides as inhibitors of HCV replication to cell-based assays capable of in situ phosphorylation.
Several attempts have been made to develop nucleosides as inhibitors of HCV RdRp, but while a handful of compounds have entered clinical development, none have proceeded all the way to registration. Amongst the problems which HCV-targeted nucleosides have encountered to date are toxicity, mutagenicity, lack of selectivity, poor efficacy, poor bioavailability, sub-optimal dosage regimes and ensuing high pill burden, and cost of goods.
There is a need for HCV inhibitors that may overcome the disadvantages of current HCV therapy such as side effects, limited efficacy, the emerging of resistance, and compliance failures, as well as improve the sustained viral response.
The present invention concerns a group of HCV-inhibiting 1-(8-hydroxy-7-(hydroxy-methyl)-1,6-dioxaspiro[3.4]octan-5-yl)pyrimidine-2,4-dione derivatives with useful properties regarding one or more of the following parameters: antiviral efficacy, favorable profile of resistance development, lack of toxicity and genotoxicity, favorable pharmacokinetics and pharmacodynamics and ease of formulation and administration. Spirooxetane nucleosides, in particular 1-(2-O,2-C-ethano-β-D-ribofuranosyl)thymine and 1-(2-O,2-C-ethano-β-D-ribofuranosyl)uracil have been described in Org. Biomol. Chem., 2003, 3514-3526. These compounds were tested against HIV, but no activity was found.
Compounds of the invention may also be attractive due to the fact that they lack activity against other viruses, in particular against HIV. HIV-infected patients often suffer from co-infections such as HCV. Treatment of such patients with an HCV inhibitor that also inhibits HIV may lead to the emergence of resistant HIV strains.